This invention relates to a fluidized nozzle and a fluidized bed system utilizing same and, more particularly, to such a nozzle and system in which a bed of particulate material in an enclosed space is fluidized by the introduction of air into the bed through the nozzle.
Fluidized bed reactors, such as gasifiers, steam generators, combustors, and the like, are well known. In these arrangements, pressurized air or other fluidizing media is passed, via a plurality of nozzles, through a bed of particulate material, including a fossil fuel such as coal and an adsorbent for the sulfur generated as a result of combustion of the coal, to fluidize the bed and to promote the combustion of the fuel at a relatively low temperature. The entrained particulate solids are separated externally of the bed and recycled back into the bed. The heat produced by the fluidized bed is utilized in various applications such as the generation of steam, which results in an attractive combination of high heat release, high sulfur adsorption, low nitrogen oxides emissions and fuel flexibility.
The most typical fluidized bed reactor is commonly referred to as a "bubbling" fluidized bed in which the bed of particulate material has a relatively high density and a well-defined, or discrete, upper surface.
Other types of fluidized bed reactors utilize a "circulating" fluidized bed. According to these processes, the fluidized bed density is well below that of a typical bubbling fluidized bed, the air velocity is greater than that of a bubbling bed and the air entrains a substantial amount of particulate solids and is substantially saturated therewith.
In both the bubbling and circulating fluidized bed arrangements, an air plenum is disposed below an air distributor plate, or grid, for supplying pressurized air to a plurality of air nozzles supported by the plate. The nozzles extend above the plate and into the bed and discharge the air into the bed.
However, the solids from the bed can backflow, or weep, through the nozzles and into the air plenum especially in connection with circulating fluidized beds when the unit is suddenly shut down while operating at full loads. As a result, the solids will accumulate in the air plenum and block air flow through the nozzles. In order to minimize the backflow, the nozzles have to be designed with great care to arrive at the best discharge angle associated with the nozzle diameter, length, bed material characteristics, etc. This is time consuming and expensive, and adds to the overall costs of the system.
This problem is compounded when the discharge angle and direction of the nozzle is especially critical, such as in fluidized beds utilizing directional and/or differential bed fluidization such as disclosed in U.S. Pat. No. 4,397,102 issued Aug. 9, 1983 and assigned to the same assignee as the present invention.